The First Principle Study Of 1111 System Iron Based High Temperature Superconductor

The zero resistance and perfect diamagnetism make superconducting materials have a broad application prospect,which has aroused the enthusiasm of people to study how to improve the superconducting critical transition temperature.After years of exploration,high critical temperature copper-oxide superconductors at liquid nitrogen temperature was found.However,there is scarce to find a suitable theory to explain the mechanism of superconductor.So the development and application of superconducting technology are seriously restricted.Until the iron-based superconductors were found it provided a new direction for the exploration of the theory of superconducting mechanism.In this paper,we study the structural properties,electronic properties and correlative interactions between electrons for Th Fe As N,La Fe As O and Sr Fe As F materials,which belong to the 1111-system.And the effects of fluorite-like spacer layer(Th N-layer,La O-layer,Sr F-layer)and Fe As-layer on the properties of the materials are explored.First,using GGA method,the structural parameters Key population and Mulliken populations of the three materials under zero pressure are calculated.Results show that the fluorite layer leads to the overall anisotropic deformation,but a significant impact on the structural parameters of the Fe As layer,that is,the Fe As layer has very strong spatial stability.Under zero pressure,the As-Fe-As bond angles of the three materials deviate from the ideal tetrahedron bond angle(109.47o),which may lead to the weaker superconductivity.At the same time,the quantitative analysis of electrons exchange of each atom in the three materials shows that the three materials show strong covalent.In the zero pressure state,the band structure of the three materials have a significant difference and some energy bands crossed the Femi level,which suggests obvious metal character.In addition,near Femi level mainly provided by Fe 3d and As 4p orbital electron.The results of elastic mechanics calculation shows that the three materials have better mechanical stability and lager mechanical anisotropy.The hardness of Th Fe As N and La Fe As O is high,which shows that they belong to hard material.And Sr Fe As F belongs to soft material.The three materials have good toughness,being beneficial to practical engineering applications.Secondly,we studied the effect of pressure on the crystal structure and electronic properties of the three materials.There is a significant difference.When the pressure is 30 GPa,the As-Fe-As bond angle of Sr Fe As F is closest to the bond angle of the ideal tetrahedron,but the change of the bond of Th Fe As N and La Fe As O is small under different pressure conditions.In addition,the calculated value of Key population shows that the covalent of Fe-As bond of Th Fe As N and La Fe As O increase,while the covalent of Fe-As bond of Sr Fe As F decreases with the increasing pressure.The comparison of band structure under different pressure shows that pressure can obviously inhibit the hole-type band of Th Fe As N and La Fe As O across the Femi surface.Finally,using the LDA+U method,we study the newly discovered Th Fe As N,investigating the effects of electronic interaction on its electronic properties.We find that the coulomb electronic interaction of Fe 3d electron can significantly inhibit the hole-type band through Femi level,and its magnetism is mainly provided by Fe 3d orbital electron.The research on the fertile material of iron-based superconductor is the basic starting point for exploring the superconductivity.Therefore,it is an important way to perfect the theory of superconducting mechanism by investigating the crystal structure and electronic properties of the parent material.